Last Night's TV - The Bill, ITV1; The Deep, BBC1

Why shouldn't this drama plod on?

Everyone seemed to be watching the police in The Bill. No sooner did they pitch up on a local estate than everyone in the vicinity turned to glare at them. When they sat down in a local café to question a witness, hoodied youths cruised past the window in a menacing fashion. And when they stopped a potential suspect for preliminary questioning, both ends of the alleyway they were in filled up with a hostile crowd. Needless to say, if there were as many people at home doing the same thing, last night's episode of the long-running police drama might not have been the penultimate ever. Perhaps there was a knowing irony in the sardonic line about the lack of community backing for the latest Sun Hill murder inquiry: "Some didn't hear anything, some didn't see anything and the rest won't say anything." "Someone gobbed on me," said a disillusioned policewoman, returning from a fruitless few hours on door-to-door inquiries. It may have been an ITV executive.

I can't honestly claim I've really done my bit to keep Sun Hill on air. It's a while since I've watched and the last time I did – when it was still a semi-soap – I wasn't perhaps as supportive as a good citizen should be towards the forces of law and order. But watching last night I couldn't help but wonder why this had been singled out for redundancy while other uniformed strands still pound the beat with full job security. It began with a dying boy, exsanguinating on a council-estate landing while Smithy tried to calm him down. Obligingly, his killer had left a museum-quality trainer print in the blood pool and the estate had been equipped with those unusually high-quality CCTV cameras beloved of television procedurals. In real life the footage from most of these cameras is about as illuminating as the live transmission of the first Moon landings – they're as crisp as simmering porridge. But in fiction the images are always beautifully clear, so it wasn't very long before one of Sun Hill's finest spotted a local hard girl, fresh out of jail and loping away from the crime scene at the critical moment. They also had broadcast quality images of a drug deal going down between the victim and two local gang-leaders.

What followed wasn't exactly The Wire, but it did hint at the dynamics of gang life on a south London estate, and the rather retrograde approach to equal opportunities taken by wannabe gangsters. If you're a woman, apparently, you can be a "link" – available to any gang member with a sexual yen – or a "wifey", which comes with marginally higher status but expectations of fidelity that, if breached, could lead to murder. Next week – the concluding episode, after which we will never read "Next week" again on these particular titles.

I was away on holiday when The Deep started, and therefore unusually reliant on "Previously" to get me up to speed. Let's see now, what have we got: "You're taking us into the hydrothermal vent!", jolting collisions and people going "arghh!" as they collide with the bulkheads, a man with a Russian accent thicker than a nuclear sub's pressure hull and Jimmy Nesbitt demanding some personal time in the middle of an emergency – "This is about my family! Five minutes all right? FIVE MINUTES!". I think I've got that straight. It's The Abyss in disguise, isn't it, though possibly without luminous alien blob things.

I lost my bearings again almost as soon as the episode started, since it featured characters too peripheral to appear in the synopsis, but it never takes very long to work things out in a drama pieced together from the clichés left over from previous similar projects. The big news this week was that a "corrosive agent was acting on the integrity of the hull" of the Volos – a humungous Russian vessel full of dead Russian mariners and an understandably morose commander. I wondered if it might be that notoriously corrosive agent common sense, since you only have to glance at the Volos to see that its constructors appear to have sourced most of their building materials from a Wickes plumbing department. It's best not to let common sense come into contact with the plot either, since it tends to fizz and melt into goo the moment that happens.

Catharine, who should have been dead but wasn't, had discovered a new kind of bacteria on the sea bed: "They metabolise cellulose and produce hydrogen with 75 per cent metabolic efficiency," she told her dazzled colleagues. Unfortunately, a reactor accident had toasted all her samples and she had to go back for more. Even more unfortunately, there were agents for the oil companies on board, and they would stop at nothing to prevent news of this limitless source of clean fuel from getting out. And they had to descend into the Acheron Trench to get fresh bugs. "Human beinks should not go down dere," said another heavily accented man – about two seconds before the commander ordered their descent. They were at the bottom when they discovered that the bugs were peeing nitric acid all over the submarine's working parts, which was especially bad news for Nesbitt, who had selflessly locked his wife out of the submersible so that he could tackle the most dangerous part of the mission. "I don't know about you lot, but I am sick to death of being underwater," he said – shortly before ominous cracks appeared in his observation bubble. He certainly spoke for me.